1. Field of the Invention
The present invention relates to an algorithm to interpolate between lines of an image.
2. Description of the Related Art
In the case where a one-frame image is extracted from a moving image signal of a video camera, a camcorder, a television set (“TV”) or a video cassette recorder (“VCR”) using an interlaced scanning method with two fields for one frame to obtain an image signal of a non-interlaced scanning method, if motion in the moving image is generated due to a time difference between a first field and a second field or a handshake or the like, a difference between respective fields is conspicuous so that a phenomenon of a step-shape or tooth-shape is generated at an edge portion of the image having the motion.
To eliminate this phenomenon, it is necessary to properly modify the image data using an interlaced scanning method. This procedure is called “de-interlace”. Such methods include an intra-field method where lines of data of one-field are interpolated to generate data of one frame, and an inter-field method where data from at least two fields are used to generate data of one frame.
The intra-field type of method may include a linear interpolation, a median filtering, a Nest Median Filter (“NMF”)/Median Averaging Filter (“MAF”), an edge-adaptive interpolation and the like. The inter-field type of method may include a motion adaptive method, a Vertical Temporal (“VT”) filtering, a Motion Compensation (“MC”), a weighted median filtering and the like. Further, the de-interlacing method may be a hybrid-type method including a method in which the lines of data of one field are interpolated to generate data of one frame, combined with a method where data of at least two frames are used to generate data of one frame. In current technology, the edge adaptive interpolation and the hybrid-type method are used frequently.
The edge adaptive interpolation based on an edge direction uses other information called “edge” in comparison to the linear interpolation, an edge line average being a simple edge-adaptive interpolation method is defined as follows.
      [Equation  1]:                      x        i            ⁡              (                  i          ,          j          ,          n                )              =                                        x            ⁢                          (                        ⁢            i                    -                      d            ^                          ,                  j          -          1                ,                              n            ⁢                          )                                +                      x            ⁢                          (                        ⁢            i                    +                      d            ^                          ,                  j          +          1                ,                  n          ⁢                      )                              2      
In Equation 1, {circumflex over (d)} is a value of a horizontal edge motion. {circumflex over (d)} is obtained using a difference value according to the following rule.
      [Equation  2]:              d      ^        =          arg      ⁢                          ⁢                        min                                    -              1                        ≤            d            ≤            1                          ⁢                  diff          ⁡                      (            d            )                              
In the Equation 2, a difference value diff (d) is calculated from the following Equation 3.diff(d)=|x(i−d, j−1,n)—x(i+d, j+1,n)|  [Equation 3]
Since a characteristic of the edge appears even in a horizontal direction as well as in a vertical direction, a contour line is not only well maintained, but also since a vertical resolution is used as information on the horizontal direction while an edge dependent interpolation (“EDI”) procedure is performed, aliasing may be better eliminated in comparison to a linear method. However, in cases where the image signal includes noise, in cases where a thin edge is provided for the background having the same brightness value, in cases where the same pattern repetitively appears, such as a check pattern, for example, in cases where an edge boundary is not clear, or in cases where the brightness value is different at the same region, for examples, de-interlacing using an edge-dependent interpolation typically erroneously estimates the edge direction thereby causing an error and an artifact in the de-interlacing procedure.